1. Field of the Invention
This invention relates to a color cathode-ray tube (CRT) including an antireflection layer on its face plate and a method of producing the color cathode-ray tube. More particularly, it relates to a color cathode-ray tube having an antireflection layer suitable for preventing reflection of external light on the inner surface of a face plate and a method of producing the color cathode-ray tube.
2. Description of the Prior Art
Since the surface of a face plate (an image display surface) of cathode-ray tubes generally has luster, the cathode-ray tubes involve the problem that external light is strongly reflected and an image displayed on the face plate surface cannot be seen easily. Particularly because display devices consisting of various cathode-ray tubes have gained a wide application as a terminal device of information systems in addition television receivers, the problem of external light reflection described above has been wide spread in the field of VDT (visual display terminals), and requirements for preventing reflection have become stronger and stronger.
Various counter-measures have so far been taken in order to prevent reflection of external light. One of them etches a glass surface by hydrogen silicofluoride so as to form corrugations having a depth of 5 to 3,000 nm and a pitch of 10 to 200 nm and thus to impart a reflection prevention function (U.S. Pat. No. 2,490,662), and another method blows an alcohol solution of alkoxysilane (Si(OR).sub.4) (where R is an alkyl group) to the glass surface and then bakes the surface so as to form corrugations consisting of a SiO.sub.2 film (Japanese Patent Laid-Open No. 118932/1986).
To prevent reflection in a high precision display tube for which high resolution is requisite and in a cathode ray tube for high definition television, a method has already been put into practical application which deposits a single layer of a metal compound such as MgF.sub.2, TiO.sub.2 or SiO.sub.2 or a polymer compound or laminates a plurality of the layers, accurately controls the film thickness and refractive index and weakens reflected light by utilizing interference of light.
However, all of the methods described above are the methods of preventing reflection which are directed to the outer surface of the face plate of the cathode-ray tube. According to the methods alone, there occurs the case where the influence of external light reflected on the inner surface of the face plate strongly appears on the surface and makes an image rather invisible.
Here, it may be conceivable to form the antireflection layer having the content described above on the inner surface of the face plate. However, phosphor must be coated on the inner surface of the cathode-ray tube, and the antireflection layer must sufficiently withstand the influence of this coating. Therefore, there are various problems. In other words, according to the method of coarsening the inner surface of the face plate by H.sub.2 SiF.sub.6 etching, there are the problems that the resulting coarse surface changes due to various chemical treatments when the phosphor is coated, and the phosphor cannot be coated flatly. In the case of the method which forms the corrugated surface by blowing the Si(OR).sub.4 alcohol solution, there is the problem that the corrugation on the surface is so vigorous that the phosphor cannot well be deposited. Furthermore, in the case of the lamination of the metal compound or the polymer compound, the film layer is generally formed by vacuum deposition or sputtering. However, there is the problem that film quality is extremely apt to modify and the reflective index drastically increases due to heat-treatment and chemical treatment when the phosphor is coated.
To solve such problems, the inventors of the present invention previously proposed a cathode-ray tube having a film which exhibits antireflection characteristics on the inner surface of the face plate and production method of such a cathode-ray tube in Japanese Patent Application No. 45374/1990.
[Problem to be Solved by the Invention]
The technique proposed previously by the present inventors is the technique which comprises coating an alcohol solution of Si(OR).sub.4 containing SiO.sub.2 added thereto on the inner surface 3' of the face plate 3 of the cathode-ray tube as shown in FIG. 5, baking the face plate to form the antireflection layer 5 consisting of a SiO.sub.2 film, and forming thereon a black matrix graphite layer 4 (hereinafter referred to as a "BM layer") and a phosphor layer 6.
However, the technique described above involves the following problems.
(1) In this case, the antireflection layer 5 exists between the inner surface 3' of the face plate 3 and the BM layer 4 as shown in FIG. 5. Therefore, the beam holes 4' of the BM layer cannot be opened accurately in a clear-cut form. Although demands for high precision color cathode-ray tubes having a small beam diameter and a fine pitch have become strong particularly in recent years, this technique cannot cope with these demands.
(2) The antireflection layer 5 exists between the inner surface 3' of the face plate 3 and the BM layer 4 as shown in FIG. 5. Therefore, the BM layer 4 appears somewhat white due to diffused and reflected light from this antireflection layer 5. Since the original function of the BM layer is to improve contrast, it must appear as black as possible.
(3) Furthermore, when the BM layer 4 is coated, the inner surface 3' of the face plate as the coated surface must be cleansed chemically by hydrofluoric acid or an alkali. If the antireflection film 5 is disposed beforehand, however, denaturation of the antireflection film 5 by the acid or the alkali might occur, and there is the limitation that sufficient washing cannot be made.